1. Field of the Invention
This invention relates to a range-finding device for use in an optical apparatus such as a camera, and more particularly to an active range-finding device capable of measuring the distance between the device and a moving object, estimating the position of the object assumed at the time of photographing the same, thereby achieving accurate distance measurement thereof. Range-finding is alternately referred to herein as "ranging".
2. Description of the Related Art
So-called active ranging devices have been used for various purposes. These devices projects distance-measuring light onto an object, receive light reflected therefrom and calculates the distance between the device and the object on the basis of a signal indicative of received light. The active type is characterized in that the measurement accuracy is proportional to the amount of received light.
In the active type ranging devices, there is a case where an object is only partially radiated with light (i.e. so-called spot eclipse has occurred). In such a case, the centroid of the spot of projected light may be deviated from that of the spot of light reflected from the object, resulting in a ranging error. As a technique for preventing a ranging error due to spot eclipse, it is known to cancel an error between the centroid of the spot of projected light and that of the spot of reflected light, on the basis of signals output from a plurality of light receiving means.
Furthermore, various techniques have been proposed for real-time measuring of a distance to a moving object to perform automatic focus adjustment. For example, Jpn. Pat. Appln. KOKAI Publication No. 63-159817 discloses a technique for measuring a distance to a moving object at regular intervals, and estimating the distance to the object at which distance the object will be photographed.
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2-149810, etc. discloses a technique for measuring a distance to an object which can move also in a lateral direction with respect to a ranging device, and calculating the speed of the movement. In this technique, a plurality of light-receiving elements are provided, distance data and element data are output in time sequence, and the movement speed of an object is calculated on the basis of the distance data and the element data. The accuracy of detection is enhanced by employing a large number of light-receiving elements and ranging points. Moreover, there is known a technique for repeatedly measuring a distance to a predetermined portion of an object and calculating the average value of the measurement results in order to enhance the accuracy of ranging.
Although in the case of the above-described technique using a plurality of light-receiving elements a ranging error due to spot eclipse can be prevented, a reduction in the amount of receiving light due to the spot eclipse cannot be prevented, resulting in a reduction in ranging accuracy.
Further, although the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 63-159817 can estimate, from distance data, the distance to the object at which distance the object will be photographed, the technique can only detect the movement of the object in the direction of the optical axis.
Moreover, although the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-149810 can detect the movement of an object in the direction of the optical axis of a photographing lens and in a direction perpendicular thereto, it requires a plurality of light-receiving elements and hence a high manufacturing cost. In addition, to detect a distance to a moving object and detect its position this known technique requires that measurement at a plurality of ranging points be repeated, with the result that a great amount of time is required for ranging.